A pipe containing a spa heating element typically is a steel pipe with flanged ends. To assemble the spa plumbing, or other plumbing including flanged pipe, it is necessary to connect the flange of the pipe to another pipe, such as a threaded polyvinyl chloride (PVC) pipe.
Union, or coupler, nuts are used to connect such pipes. Conventional union nuts have an internal flange, or collar, to retain the flange of the pipe and press the flange against the end of the threaded pipe. Because the collar of a conventional union nut has an inside diameter smaller than the outside diameter of the pipe flange, union nuts are conventionally slipped onto a length of steel pipe before the flanges are formed on the ends.
Fabrication of the flanges is hampered by the presence of the union nuts. Shipping, storage, and handling of the pipe is inconvenient. If a union nut installed on a flanged pipe is accidentally broken or damaged, the entire pipe may be useless.
Because of the above problems, union nuts that can be installed on a pipe already having flanged ends have been developed. There are two-part, or split, nuts and nuts with a very narrow collar that can be forced over the pipe flange. both these types of union nuts have shortcomings.
Split nuts are formed in two halves that are sandwiched onto the flanged pipe then connected together, such as with screws. Split union nuts have been manufactured by injection molding. They have the disadvantage that the two halves tend to deform away from perfect semi-circularity. When the halves are mated, the threads do not match up perfectly, making the union nut difficult to connect to the threaded pipe. The split union nuts are not as strong or reliable as unitary nuts. Also, additional parts, such as screws, are needed, as well as the tool to install them.
Union nuts have been made with a narrow, deformable flange-retaining collar so that the flange of the pipe can be forced through the central bore of the collar at an angle. Obviously, such a design allows very little overlap of the pipe flange and the union nut collar. Narrow collar nuts have a variety of leakage problems and they are not reliable enough for many applications.
There is thus a long-felt need for a union nut that is as strong and reliable as conventional union nuts and that can be installed on pipes already having flanged ends. There is a need for such a union nut that is easy to install correctly every time without tools.